#include<cstdio>
#include<iostream>
#include<cstring>
#include<cstdlib>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
#include<ctype.h>
#include<sys/stat.h>
#include<fcntl.h>

#define COMMAND_SIZE 1024
#define FORMAT "[%s@%s %s]# "

//shell内部维护的全局数据
#define MAXARGC 128
char* g_argv[MAXARGC];
int g_argc = 0;

#define MAX_ENVS 100
char* g_env[MAX_ENVS];
int g_envs = 0;

#define NONE_REDIR 0
#define INPUT_REDIR 1
#define OUTPUT_REDIR 2
#define APPEND_REDIR 3

int redir = NONE_REDIR;
std::string filename;

char cwd[1024];
char cwdenv[1028];

int lastcode = 0;

const char* GetUserName()
{
	const char* name = getenv("USER");
	return name == NULL ? "None" : name;
}

const char* GetHostName()
{
     const char* hostname = getenv("HOSTNAME");
     return hostname == NULL ? "None" : hostname;
}

const char* GetPwd()
{
	//const char* pwd = getenv("PWD");
	const char* pwd = getcwd(cwd, sizeof(cwd));
	if(pwd != NULL)
	{
		snprintf(cwdenv, sizeof(cwdenv), "PWD=%s", cwd);
		putenv(cwdenv);
	}
	return pwd == NULL ? "None" : pwd;
}

const char* GetHome()
{
	const char* home = getenv("HOME");
	return home == NULL ? "" : home;
}

bool Cd()
{	
	if(g_argc == 1)
	{
		std::string home = GetHome();
		if(home.empty()) return true;
		chdir(home.c_str());
	}
	else
	{
		std::string where = g_argv[1];
		//cd -   cd ~
		if(where == "-")
		{
			//TODO
		}
		else if(where == "~")
		{
			//TODO
		}
		else
		{
			chdir(where.c_str());
		}
	}
	return true;
}

void Echo()
{
	if(g_argc == 2)
	{
		//echo "string"
		//echo $?
		//echo $PATH
		std::string opt = g_argv[1];
		if(opt == "$?")
		{
			std::cout<< lastcode << std::endl;
			lastcode = 0;
		}
		else if(opt[0] == '$')
		{
			std::string env_name = opt.substr(1);
			const char* env_value = getenv(env_name.c_str());
			if(env_value)
				std::cout<< env_value << std::endl;
		}
		else
		{
			std::cout<< opt << std::endl;
		}
	}
}

std::string Dirname(const char* pwd)
{
#define SLASH "/"
	std::string dir = pwd;
	if(dir == SLASH) return "/";
	auto pos = dir.rfind(SLASH);
	if(pos == std::string::npos) return "BUG?";
	return dir.substr(pos+1);
}

void MakeCommandLine(char cmd_prompt[], int size)
{
	snprintf(cmd_prompt, size, FORMAT, GetUserName(), GetHostName(), Dirname(GetPwd()).c_str());
}

void PrintCommandPrompt()
{
	char prompt[COMMAND_SIZE];
	MakeCommandLine(prompt,sizeof(prompt));//读入
	printf("%s",prompt);//打印
	fflush(stdout);
}

bool GetCommandLine(char* out, int size)
{
	char* c = fgets(out,size,stdin);
	
	if(c==NULL) return false;
	out[strlen(out)-1] = 0;//清理\n
	if(strlen(out) == 0) return false;
	return true;
}

//3.命令行分析 "ls -a -l" -> "ls" "-a" "-l"
bool CommandParse(char* commandline)
{
#define SEP " "//必须是双引号,因为strtok参数char*
	g_argc = 0;
	g_argv[g_argc++] = strtok(commandline, SEP);
	while((bool)(g_argv[g_argc++] = strtok(nullptr, SEP)));
	g_argc--;
	return g_argc > 0 ? true : false;
}

void PrintArgv()
{
	for(int i = 0; g_argv[i]; i++)
	{
		printf("argv[%d]->%s\n", i, g_argv[i]);
	}
}

bool CheckAndExecBuiltin()
{
	std::string cmd = g_argv[0];
	if(cmd == "cd")
	{
		Cd();
		return true;
	}
	else if(cmd == "echo")
	{
		Echo();
		return true;
	}

	return false;
}

int Execute()
{
	pid_t id = fork();
	if(id == 0)
	{
		int fd = -1;
		//检查子进程重定向
		if(redir == INPUT_REDIR)
		{
			fd = open(filename.c_str(), O_RDONLY);
			if(fd < 0) exit(1);
			dup2(fd, 0);
		}
		else if(redir == OUTPUT_REDIR)
		{
			fd = open(filename.c_str(), O_CREAT | O_WRONLY | O_TRUNC, 0666);
			if(fd < 0) exit(2);
			dup2(fd, 1);
		}
		else if(redir == APPEND_REDIR)
		{
			fd = open(filename.c_str(), O_CREAT | O_WRONLY | O_APPEND, 0666);
			if(fd < 0) exit(2);
			dup2(fd, 1);
		}
		else
		{}

		//进程替换不影响重定向的结果。
		//child
		execvp(g_argv[0], g_argv);
		exit(1);
	}
	int status = 0;
	//father
	pid_t rid = waitpid(id, &status, 0);
	if(rid > 0)
	{
		lastcode = WEXITSTATUS(status);
	}
	return 0;
}

void TrimSpace(char cmd[], int& end)
{
	while(isspace(cmd[end]))
	{
		end++;
	}
}

void RedirCheck(char cmd[])
{
	redir = NONE_REDIR;
	filename.clear();
	int start = 0, end = strlen(cmd)-1;

	while(end > start)
	{
		if(cmd[end] == '<')
		{
			cmd[end++] = 0;
			TrimSpace(cmd, end);
			redir = INPUT_REDIR;
			filename = cmd+end;
			break;
		}
		else if(cmd[end] == '>')
		{
			if(cmd[end-1] == '>')
			{
				// >>
				cmd[end-1] = 0;
				redir = APPEND_REDIR;
			}
			else
			{
				// >
				redir = OUTPUT_REDIR;
			}
			cmd[end++] = 0;
			TrimSpace(cmd, end);
			filename = cmd+end;
			break;
		}
		else
		{
			end--;
		}
	}
}

int main()
{
	while(true)
	{
		//1.打印命令行
		PrintCommandPrompt();

		//2.获取用户的命令
		char commandline[COMMAND_SIZE];	
		if(!GetCommandLine(commandline, sizeof(commandline)))
			continue;

		//3.重定向分析 "ls -a -l > file.txt" -> "ls -a -l" "file.txt" -> 判定重定向方式
		RedirCheck(commandline);
		
		printf("redir: %d, filename %s\n", redir, filename.c_str());

		//4.命令行分析
		if(!CommandParse(commandline))
			continue;
		//PrintArgv();

		//5.检测并处理内键命令
		if(CheckAndExecBuiltin())
			continue;


		//6.执行命令
		Execute();
	}

	return 0;
}
